Youtube has some video's on how to use calls to lure a fox or coyote. I'm happy to hear your chickens are safe.Here is a link to a call sold on Amazon...
To be safe let your chickens out at different times and do the same when you lock them up. Foxes will watch you and learn your habits .They're cunning! Its not unusual for one to grab one soon as you go inside.Sorry for your loss!
I agree with getting a dog or an electric fence to get rid of the fox .The only thing worse than a persistent fox is a family of them hunting your chickens together.They can have dens miles apart and are hard to get rid of.